I can tell you, I had the same corals as the ones on Lasse’s picture, I wanted them out. I took the rocks out of the tank, kept them on the back deck for 3 weeks. After 3 weeks, I took the rocks in the bathtub and scrubbed them with tap water and a brush, nasty stuff was still present, I woke up at 3 Am with a fever, uncontrollable shakes, my body wanted to throw up, I was hot and cold at the same time. It happened to me, I thought I was safe after 3 weeks of rocks being in sun and air... nope. I spent a few hours in the hospital, left around 8 am. Wasn’t sick before or after.
I love Zoas, but my wife puts her foot down, after that incident, I am not allowed. The scenario is real, I lived through it.